There are several main categories into which kernel releases may fall:

Prepatch

Prepatch or "RC" kernels are mainline kernel pre-releases that are
mostly aimed at other kernel developers and Linux enthusiasts. They
must be compiled from source and usually contain new features that
must be tested before they can be put into a stable release.
Prepatch kernels are maintained and released by Linus Torvalds.

Mainline

Mainline tree is maintained by Linus Torvalds. It's the tree where
all new features are introduced and where all the exciting new
development happens. New mainline kernels are released every 2-3
months.

Stable

After each mainline kernel is released, it is considered "stable."
Any bug fixes for a stable kernel are backported from the mainline
tree and applied by a designated stable kernel maintainer. There are
usually only a few bugfix kernel releases until next mainline kernel
becomes available -- unless it is designated a "longterm maintenance
kernel." Stable kernel updates are released on as-needed basis,
usually once a week.

Longterm

There are usually several "longterm maintenance" kernel releases
provided for the purposes of backporting bugfixes for older kernel
trees. Only important bugfixes are applied to such kernels and they
don't usually see very frequent releases, especially for older
trees.

Longterm release kernels

Version

Maintainer

Released

Projected EOL

4.19

Greg Kroah-Hartman

2018-10-22

Dec, 2020

4.14

Greg Kroah-Hartman

2017-11-12

Jan, 2020

4.9

Greg Kroah-Hartman

2016-12-11

Jan, 2023

4.4

Greg Kroah-Hartman

2016-01-10

Feb, 2022

3.16

Ben Hutchings

2014-08-03

Apr, 2020

Distribution kernels

Many Linux distributions provide their own "longterm maintenance"
kernels that may or may not be based on those maintained by kernel
developers. These kernel releases are not hosted at kernel.org and
kernel developers can provide no support for them.

It is easy to tell if you are running a distribution kernel. Unless you
downloaded, compiled and installed your own version of kernel from
kernel.org, you are running a distribution kernel. To find out the
version of your kernel, run uname -r:

# uname -r
3.7.5-201.fc18.x86_64

If you see anything at all after the dash, you are running a distribution
kernel. Please use the support channels offered by your distribution
vendor to obtain kernel support.